Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1992-06-30
1993-03-16
Cross, E. Rollins
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9033, 123 9036, 123 9046, F01L 124
Patent
active
051934973
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for controlling the take-up of valve clearance in the valve mechanism of an internal combustion engine, comprising, on the one hand, a rocker arm system with at least one typically hollow-formed rocker arm shaft and, on the other hand, a hydraulically operated take-up means arranged in connection with the operating end of those valves whose valve clearance is to be taken up, whereby each valve's rocker arm has a conduit for the supply of oil to the take-up means, and the drainage of the oil fed to the rocker arm shaft and thence to the rocker arms and respective take-up means is arranged such that only a small quantity of the oil, i.e. that which is necessary for the bearing surfaces of the rocker arms, is drained via normal leakage flow between the rocker arms and their shaft.
BACKGROUND AND PROBLEM
Known devices for valve clearance take-up have up until now above all been used specially for this purpose, that is the take-up of clearance, both so as to achieve a quieter running of the engine and to reduce the stresses therein. Such a device is known, for example, from GB-A-2 138 093.
The ever growing demands over the last few years for more effective auxiliary braking systems on commercial vehicles has led to ever more advanced solutions to satisfy the demands. One of these is described in Swedish patent application 8900517-7 (and WO-A-90/09514). According to this document the camshaft of the engine's valve system is used to obtain negative work from the engine instead of positive work which it is normally intended to achieve. This is achieved with the aid of extra lobes on the camshaft which open a connection between the engine's combustion chambers and its exhaust system during the latter portion of the inlet stroke (four-stroke motor) and by closing this connection at the first portion of the corresponding compression stroke. In this way, a large portion of the compression work is lost as braking. The said additional lobes on the camshaft are so small that in terms of size they fall into the category which can be called normal clearance in an engine of this type. Another engine-braking device is described in EP-A-0 269 605 in which valve clearance take up means are located in a recess in the cylinder-head of an internal combustion engine directly beneath the end of the rocker arm remote from the valve stem.
Known methods and devices for actively adjustable valve clearance take-up include separate systems for the activation and de-activation, controlled either by electrical systems or by separate hydraulic systems No matter which type is chosen, a relatively high grade of complexity is required, particularly with the implementation of a separate hydraulic system. In addition to the fact that this means almost a doubling of the number of hydraulic components in the valve system, a result thereof is the reduced reliability and a larger production cost per unit.
SOLUTION
A principal object of the present invention is to provide device whereby the engine's existing pressurized oil system is used in order to guarantee the above mentioned function with minimal modification using essentially already existing components.
At the same time it is an object to facilitate a comparatively lower production cost per unit with maintained or improved reliability of the function by means of said optimisation of the use of the engine's existing components.
ADVANTAGES
Practical trials have shown that, with the invention described by way of introduction, exceedingly good operation in all respects is achieved. The device according to the invention is characterized in that a quantity of the oil fed to the rocker arm shaft is drained from the rocker arm shaft back to the engine oil reservoir via a specially arranged conduit having an outlet orifice, and in that a pneumatically or mechanically operable piston-cylinder unit is arranged close to said outlet orifice to effect closing of said orifice, thereby causing an increase in the pressure in the rocker arm sha
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W. J. Polizzoni, "Dyntard . . . Mack's New Engine Brake", Feb. 15, 1971 in Automotive Industries on pp. 49-50, vol. 144, No. 4.
AB Volvo
Cross E. Rollins
Lo Weilun
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